The present invention relates to the allocation of resources in a communication system. It relates more particularly to the allocation of resources among a set of resources shared in a radiocommunication system.
Numerous methods of allocating resources are known. Among them may be mentioned, by way of example, the “round robin” method in which the resources are allocated to serve various users in turn.
A method of allocation such as “round robin” may make it possible to distribute the resources equitably between the various users, by assigning them one and the same priority level. Thus, the same quantity of data will be transmitted to each user over a transmission time period.
Such a method, well suited to wire networks, cannot however be applied satisfactorily in a radiocommunication network. In such a network, in fact, the propagation channels vary continuously, as a function of the radio conditions, so much so that it is very difficult to ensure a constant throughput for a user, and a fortiori, equity in the quantity of data transmitted to the various users over a transmission time period.
Specifically, if the radio link of a given user is very degraded, the data transmitted over this link will not be able to be decoded correctly when they are received by this user. Equity will then no longer be complied with. Furthermore, communication resources will have been used needlessly, whereas they could have been exploited to transmit data destined for a user furnished with a radio link of better quality.
Other methods of allocating resources are also known and are used in radiocommunication networks. These methods take account of the quality of the radio links, basing themselves for example on a signal-to-interference (C/I) ratio.
FIG. 1 illustrates an exemplary allocation according to such a method. The upper part of the figure depicts data packets D1-D4 to be transmitted to four respective users U1-U4. Thus, the data D1 will be required to be transmitted to the first user U1, the data D2 to the second user U2, D3 to U3 and D4 to U4.
The same priority level is assigned to each user. On the other hand, the users have radio links of different quality. To simplify the example, it is considered that the quality of a radio link is represented by a parameter indicating the number of data packets that can be received by the corresponding user during a transmission time interval. In this example, it is considered that this parameter has a value Q1=5 for the user U1, this signifying that U1 will be able to receive five data packets D1 at most, at each transmission time interval. Likewise, the parameters Q2-Q4 corresponding respectively to the quality of the radio links associated with the users U2-U4, have the following values: Q2=2, Q3=6 and Q4=3.
The lower part of FIG. 1 represents the data transmitted, as a function of the resources allocated, for each transmission time interval. The number of data packets that can be transmitted at each interval has been fixed at 8 in this example. U3 has the radio link of better quality, 6 communication resources will therefore be allocated to the said user by priority, during the first transmission time interval t1, so that 6 data packets D3 can be transmitted to this user, that is to say the maximum number of packets for the latter, by virtue of the quality on the corresponding link (Q3=6). The 2 remaining resources for this interval t1 will be allocated to U1 who has the second best quality link (Q1=5). During the subsequent transmission time intervals t2, t3 . . . , the same allocation of resources will be made, as illustrated in FIG. 1, as long as the parameters Q1-Q4 remain unchanged and as long as there are still data to be transmitted to the users U1 and U3.
It is therefore noted, in this example, that only the users U1 and U3, who benefit from a radio link of good quality, can receive data over a certain time period. Furthermore, although the quality of the links associated with the users U1 and U3 differs little (Q1=5 and Q3=6), U3 receives three times as much data as U1 over the same time period.
Such a method of allocating resources, which favours the users furnished with a radio link of good quality, is not satisfactory either, since it is greatly prejudicial to certain users, who would yet be able to receive a substantial quantity of data, in favour of a restricted number of other users.
Furthermore, other constraints are sometimes neglected in certain known methods of allocating resources. This includes for example the number of resources actually available at the radio transmitter level, the type of data transmitted (identical processing of the first transmissions and of the retransmissions may be damaging in certain cases), or else the reception capabilities of the user terminals (certain terminals may not receive data at each transmission time interval for example).
An object of the present invention is to limit the abovementioned drawbacks, by allocating the resources according to an effective compromise between a certain level of equity between the users and the taking into account of the radio conditions existing on the corresponding radio links.
Another object of the invention is to propose an allocation of the resources that is well suited to radiocommunication systems comprising a set of resources to be shared between various users.
Yet another object of the invention is to improve the effectiveness of the allocation of resources, by taking account of other constraints neglected in the currently known methods of allocation.